Switched mode power supplies are known in a wide variety of developments and are used to connect electrical loads to a power grid or to a power source. A distinction is made for example between switched mode power supplies, which operate as blocking oscillator converters, push-pull converters or as flux converters, etc. Electrical energy is transmitted via a transformer from a primary side to a secondary side. The voltage applied at the primary side is clocked in the process by means of a switching element, the clock frequency corresponding to a multiple of the mains frequency. The transformer can accordingly be small owing to the high clock frequency.
It should be noted in this connection that heat is produced in the components of a switched mode power supply, which has to be dissipated using separate means so the temperatures of individual components does not reach a critical value. Moreover, the power that can be transmitted by a switched mode power supply is dependent on the temperature of individual components.
The generation of heat in the transformer, switching element and in the secondary-side rectifier diode should be observed in particular.
According to the prior art different methods are known for dissipating the heat produced in a switched mode power supply. The energy that needs to be expended to operate any cooling devices that may be provided should be noted in this connection.
Thus US 2003/0107907 for example describes a switched mode power supply which uses the parasitic energy of the switching element to drive a fan.
However, the use of fans, known from the prior art, to increase the cool air throughflow in switched mode power supply casings has the drawback that the components arranged in the casing are quickly soiled by various air-borne particles. This can impair operatability, for which reason a dust filter is usually arranged at the ventilation inlet of the casing. This leads to increased expenditure on maintenance, however, as these dust filters have to be regularly replaced.
According to the prior art natural air convection is usually used for cooling switched mode power supplies. In this case ventilation apertures are arranged in the switched mode power supply casing, via which heated air can escape upwards and fresh air can flow in from below. The arrangement of the heat-generating components inside the casing is usually guided by the prevailing flow conditions. JP 2001 095 233 for example describes the arrangement of a plurality of converter modules inside a switched mode power supply casing. The higher-power converter modules are cooled more effectively by this arrangement than the lower-power converter modules.
In addition heat sinks may be arranged, which are thermally connected to components for cooling and dissipate heat to the environment. JP 2005 033 088 for example describes the arrangement of cooling ribs that project from a casing and thus dissipate heat from switched mode power supply components to the environment.
Other known measures for cooling switched mode power supplies relate to the configuration of individual heat-generating components. US 2004/0080393 thus discloses a ring transformer for use in switched mode power supplies in which the winding material is advantageously arranged for heat dissipation.
JP 2006041314 A1 also describes a specific development of the winding material for transformers in a switched mode power supply. In this case the secondary winding of the transformer is formed as a heat pipe, whereby good heat transfer is achieved even with low convection. The expenditure on construction and the restriction in the design of the transformer should be noted in this connection, however.